In the medical field, various types of implantable medical electrical leads are known and used. For example, implantable medical devices (IMD) such as cardiac pacemakers, cardioverters, or defibrillators commonly have one or more implantable medical leads connecting the device to cardiac tissue. The leads coupling the devices to the cardiac muscle are commonly used for delivering an electrical pulse to the cardiac muscle, for sensing signals indicative of a physical parameter that may be produced in the cardiac muscle, or for both delivering and sensing.
The leads are susceptible to categorization according to the type of connection they form with the heart. An endocardial lead includes at least one electrode at or near its distal tip adapted to contact the endocardium (i.e., the tissue lining the inside of the heart). An epicardial lead includes at least one electrode at or near its distal tip adapted to contact the epicardium (i.e., the tissue lining the outside of the heart). Finally, a myocardial lead includes at least one electrode at or near its distal tip inserted into the heart muscle or myocardium (i.e., the muscle sandwiched between the endocardium and epicardium).
The lead typically consists of a flexible conductor surrounded by an insulating tube or sheath that extends from the electrode at the distal end to a connector pin at the proximal end. Some leads have multiple spaced apart distal electrodes at differing polarities and are known as bipolar type leads. The spacing between the electrodes can affect lead performance and the quality of the electrical signal transmitted or sensed through the heart tissue.
With the advancement in treatment of certain heart conditions such as congestive heart failure (“CHF”), there is often a need to perform multi-chamber stimulation. For example, cardiac resynchronization therapy (“CRT”) (also commonly referred to as biventricular pacing) is one treatment for heart failure, which requires stimulation of right and left chambers to increase cardiac output. A common approach for accessing the left side of the heart is a transseptal access from the right atrium through the intra-atrial septum to the left atrium. U.S. Pat. No. 7,678,081, and U.S. Patent Application Publication 2007/0083168, both of which are incorporated herein by reference in their entirety, provide examples of catheter systems employing a right to left atrial transseptal approach. Once so inserted in a left side chamber, the distal end of the lead is positioned and often secured to tissue.
Typically, the distal end of a lead is electrically coupled with the endocardium by either an active anchoring mechanism or a passive anchoring mechanism. Passive anchoring mechanisms, such as a tine assembly, lodge or passively fix the lead to the heart. Active anchoring mechanisms use a structure, such as a helix or hook, to engage into or actively fix themselves to the heart.
While a large number of anchoring systems and methods are presently available, there remains a need for an improved medical electrical lead and attachment system suitable for minimizing shunting between chambers and minimizing lead motion for leads where access to target tissue may require puncturing through tissue, such as left-sided cardiac lead placement through a septal wall.